Numerous electromagnetic accelerators have been designed for the purpose of providing projectile propulsion. An example of such an accelerator is a electromagnetic coaxial launcher (ECL) disclosed in Kolm et al, "Basic Principles of Coaxial Launch Technology," IEEE Transactions on Magnetics, Vol. Mag-20, No. 2, pp. 227-230 (March 1984). That launcher employs a pair of coaxial coils to generate a traveling solenoidal magnetic field. The ECL includes a segmented stationary drive coil which extends over the length of the coaxial accelerator and generates a traveling magnetic field therein. A second coil, mounted on the projectile, generates a static magnetic field which interacts with the travelling magnetic field of the drive coil. The projectile coil is activated either by pulsing the drive coil to induce current in the projectile coil or by direct electrical connection via brushes to the drive coil. The projectile is propelled the length of the coaxial accelerator by the repulsion force produced between the traveling magnetic field of the drive coil and the static magnetic field of the projectile coil. Thrust is determined by the amount of drive current applied. The drive current comprises pulses which must be precisely synchronized with the transit of the projectile coil through each drive coil. Consequently, the voltage of the system must increase as the velocity of the projectile increases and a high voltage commutation capability must, therefore, be provided. This is a major disadvantage of the ECL in that high launch velocities cannot, in general, be achieved due to limitations in high voltage commutation technology.
Another example of an electromagnetic launcher, the helical launcher, uses a continuous helix as the drive coil. This launcher is described in Mongeau, "Analysis of Helical Brush commutation," IEEE Transactions on Magnetics, Vol. Mag-20, No. 22 (March 1984). The interior surface of the continuous helix provides a linear commutating surface. Sliding brushes attached to the projectile excite a limited section of the drive helix. In the helical launcher, the projectile coil is excited by conventional slip rails. Since a projectile coil is required, and high voltage commutation is thus needed, the helical launcher is subject to limitations similar to those suffered by the ECL.
Other projectile accelerators of possible interest include that disclosed in U.S. Pat. No. 4,432,333 (Kurherr) which discloses a multi-coil electromagnetic projectile accelerator.
In addition to the disadvantages imposed by the need to provide high voltage commutation, previous electromagnetic projectile launchers suffer from other problems such as arcing, melting, and projectile deformation caused by the high induction in the coils.